Electrolytic recording paper



Patented Apr. 28, 1942 ELECTROLYTIC RECORDING PAPER Paul Talmey, New York, N. Y., a ssignor to Radio Inventions, Inc., New York, N. ,Y., a corporation of New York Application February 25, 1939, Serial No. 258,391

2 Claims.

The present invention relates to an electrochemical recording medium suitable for use in facsimile recorders and the like.

One object of the present invention is to provide an' electro-chemical recording medium capable of producing a record of high optical contrast and maximum density and with a high order of detail.

Another object is to provide an electro-chemical recording medium in which drag or tailing effects are eliminated.

A particular object is to provide an electrochemical recording medium substantially permanently stable toward light and thermal effects yet capable of efliciently utilizing relatively high electrical currents for the marking thereof.

Other objects are set forth in the copending application entitled Electrolytic recording paper, Serial No. 31,564, filed July 16, 1935 (now Patent Number 2,173,141 issued September 19, 1939) and to which this is to be considered a continuation in part. Certain features to be set forth below are also shown in the copending application entitled "Electrolytic recording paper and process, Serial No. 56,318 filedon December 27, 1935 in which certain molybdenum and tungsten compounds are disclosed.

Facsimile recording may be practiced in a number of ways as follows:

1. Records may be printed from an inkedmember or carbon paper as an -electro-mechanical impression.

2. Records may be made by rendering transparent a light-colored opaque layer covering a darker layer on a prepared paper, usually by burning off the upper layer by means of an electric spark.

3. Records may be printed on a light-sensitive medium from a lamp fed with. facsimile sig-' nals.

4. Records may be printed by oxidizing a light this case the marking takes place at the cathode. F

It has been found that when all the important characteristics of a recording medium, such as permanence, contrast, detail, simplicity and cost are taken into consideration that the last two methods offer the best solution to the recording effects providing photo-sensitive materials are not used.

sensitizing substances for electro-chemical reducing recording have been found to mark most easily when in. an acid condition. If the acidity is too great, however, a paper supporting medium will be destroyed or the record will fade. If the substance exhibits strong buffer characteristics, that is, a strong resistance to change in pH (function of hydrogen ion concentration), it is possible to reduce a large percentage of the sensitizing substance starting with an acidity low enough not to injure a paper support without producing a reduction in acidity to a point where further reduction is blocked. If the sensitizing substance is insoluble and the reduced product is insoluble, fading and other deleterious effects, such as loss of detail due to drag are eliminated. The lighter the color of the initial substance and the darker the final reduced product, the greater will be the contrast of the resulting record. The oxyhalides and other compounds of antimony and bismuth have been found to fu1- fill the above requirements, as more fully set forth below.

The figure of the drawing shows a titration curve of antimony trichloride against sodium hydroxide and of a completely dissociated acid and hence the pH of pure water or a'solution of certain salts as set forth above is 7. Substances or solutions having values of pH of less than i are said to be acid, due to an excess of hydrogen ions, while substances or solutions having values of pH of more than 7' are said to be basic, due to an excess of hydroxyl ions. Further, if a weak acid, such as acetic acid, is allowed to react with a'strong base, such as potassium hydroxide, a salt having a basic reaction is produced. The reaction is as follows:

forming the normal salt KAC having basic char combine with the hydroxyl ion formed by the ionization of the water, since potassium hydroxide ionizes almost completely, whereas the acetate ion will combine with the hydrogen ion removing it from solution and leaving an excess of hydroxyl ion. Thus, we may have a normal salt with a basic characteristic. Similarly, we may have a normal salt with an acid characteristic formed by a reaction betweena weak base and a strong acid. In addition, there are basic salts which are salts whose solution has a higher pH than the normal salt, althoughthis pH may still be less than '7. Thus, antimony oxychloride (SbOCl), a basicsalt, is more basic than antimony trichloride (SbCla), the normal salt, yet SbOCl has a pH of 3.0 in saturated solution which is well on the acid side.

The term buifer is used to describe an important characteristic of the final coatings to be utilized, according to the present invention. A titration curve (see the figure of the drawing) is a graphical representation of pH plotted against some added reagent. If this curve shows no points of inflection slope (see curve b), it shows that only normal compounds are being formed, or that the reaction has been completed. On'the other'hancl, if the slope of the curve becomes less steep at some point, it indicates the start of an intermediate chemical reaction and a resumption of the initial slope indicates the completion oi this reaction. These decreases in slope of the pH curve show resistance to a change in pH and are called bufier points. A buffer may be defined as a compound which resists a change in pH as shown by an intermediate region of decreased slope in the pH curve. A buffer may also be defined as a substance which, if added to-another substance, causes the resulting substance to resist changes in pH. In general, the stronger the buiier action, the longer and flatter will be the portion of the pH curve associated with the bufier action.

In electro-chemical recording utilizing reducing efi'e'cts of an electric current, one effect of the current is to increase the pH of the recording medium at the cathode. It has been found, however, that ii the pH becomes greater than about 5, then the mark produced by the recorder will become increasingly faint. On the other hand, if the recording medium has too low a pH, the paper supporting the medium will be darkened or destroyed. Thus, it will be appreciated that a mits higher initial pH preserving the paper and also permits the use of a higher recording current producing a denser mark before the pH is raised to a point where recording becomes diflicult or impossible. i

The figure oi the drawing shows a titration curve a of antimony trichloride which at certain points of the curve exhibits strong buil'er characteristics. The SbCh is titrated against cubic centimeters of 2.25 normal NaOH starting with cubic centimeters of a solution of SbCla containing 22.4 grams of the latter. The pH curve starts out at a little over 3 at point 1, drops rapidly to about 1.4 at point 8, is flat to point 9,

rises to point l0, rises less rapidly to point H,'

rises rapidly to point I2, is very flat to point l3, rises to point I, is flat to point l5, rises gradually to point It, rises rapidly to point I1, is flat to point It, and then rises very rapidly to point N. The vertical arrows indicate points where calculations show new products are completely formed and tall as would be expected at the ends of flat or nearly flat portions of the curve. Flat tion of SbOCl, the gradual rise from points to it indicates the formation of Sb405C12, and the flat from points ii to It indicates the formation of SbzOa. As pointed out above, marking by electro-chemical reduction tends to increase the pH and if the pH rises above about 5, marking becomes very dimcult. Hence, if the sheet to be marked contains Sb405Cl2, as formed in the region or point it on the titration curve, the buffer action as shown between points ii and it will resist an increase in pH permitting higher recording currents and hence denser markings in the recording process than would be possible without the buffer action. Point it thus indicates a region where a, large percentage of reducible material is present (SbiOtCh) followed by a bufier region.

Curve b shows for comparison the theoreti cal titration of a completely dissociated acid (0.293 gram equivalents in 10 cubic centimeters of aqueous solution) titrated against cubic centimeters of 2.25 normal NaOI-I solution. The first part of this curve up to a pH of about 1.0 has a lower slope indicating chemical reaction (simple neutralization in this case) while above 1.0 the recording medium which in itself has strong buffer characteristics, the advantages or the buffer action may be obtained to a somewhat medium having strong buffer characteristics perlesser degree by the addition of an ancillary buiier. Also, a medium exhibiting weak buffer characteristics may have its buffer action increased by the addition of ancillary buiiers. The following compounds may be used as ancillary buffers: molybdenum trioxide, stannic chloride, stannous chloride, gallic acid, salycilic acid, benzoic acid and other acids, such as citric, boric and phosphoric, of slightly dissociated charactr which have buffer characteristics and may be brought by partial neutralization to a pH of over 3. Note, however, that the interaction of stannous chloride and molybdenum trioxide produces a "dark blue discoloration and the two should not be used simultaneously. Likewise, gallic acid reacts with molybdenum trioxide to form a strawcolored discoloration.

Antimony oxychloride of the formSbrOsClz is white, thermal and photo stable, insoluble, a strong butler and has a suitable pH for use on a paper record sheet. Many other compounds, of antimony and bismuth are white, thermal and photo stable, insoluble, have or may readily be brought to a suitable pH, and have suflicient buffer action or may readily be made to have satisfactory bufler characteristics by the addition of an ancillary buffer as set forth above. Some of these antimony and bismuth compounds are as lollows:

All of the above compounds are reducible at the cathode of an electric-circuit to a dark colored lower oxide or the metallic element itself. These are all basic salts of antimony or bismuth and while other basic salts are known to exist and may be used in electrolytic recording,'they have.

been omitted from the list either because they were colored or not readily obtainable. Since these compounds may be readily tested for their desirable qualities in electrolytic recording, once they are obtained, this is felt to be a complete disclosure of the basic salts of antimony and bismuth, organic and inorganic suitable for electrolytic recording.

Other compounds of antimony and bismuth are also reducible to dark colored substances. In general, they mark more slowly than the basic salts, due to lack of buifer action or even alkalinity. The tri-valent compounds are usually more easily reduced than the penta-valent compounds. Below is shown a list oi these compounds with brief remarks as to their characteristics. With the use of an ancillary bufier, their characteristics, as far as ease and speed of electrolytic marking goes, are greatly improved.

Compound Remarks Antimony tribromide (SbBri) Antimony triiodide (SbIa) Antimony oxilodide precipitates from so] tion. a. Antimony oxide (SbgOg) Very insensitive. Potassium antimoniatc (diapho- Sensitive.

re 10 Tartar emetic Dissolved in H0].

Potassium antimoniatc (pyro)- Antimony oxybror'nide precipitates from solution.

Reduction products redissolve rapidly.

Antimony pentasulfide; Orange coat. Bismuth subcarbonatc insensitive. Bismuth lactate Solidmark. Bismuth chromate Orange coat. Bismuth subiodide insensitive.

Yellowish coat.

Bismuth tartrate Poor mark. Bismuth ammtonium citrate 000% mark.

Do. Good mark (insensitive).

- paper pulpin the process of manufacture, coating on the paper or forming by chemicalreactions within the pores of the paper. Various substances may be added to the primary comwith the gelatin or other binder to eliminate foam and produces a smoother coat. Glycerine or any glycerine substitute, such as sorbitoP' may be added to act primarily as a plasticizer. Chrome alum or anychrome salt of the same valency or which may be brought to the same valency may be added to the coating in order to increase the water-resistance of a gelatin binder. Formaldehyde or other aldehydes or any compound which liberates an aldehyde, such as hexamethyleneamine may be added to the coat and increases the water resistance of the binder and with the chrome salts gives a result which is in excess of what would be expected if the chrome salt and the formaldehyde acted as an aggregate. Lubrication, tofacilitate marking with a moving electrode, may be added to the medium by adding Proofit or other emulsions containing wax or fatty substances. The above added substances may have beneficial actions other than those noted. For instance, gelatine may be used as an ancillary buffer, it previously treated with a weak solution of an acid such as hydrochloric.

In order to render the recording medium electrically conductive, so that electrolytic recording may be readily practiced, an electrolyte with sufficient water to render it conductive may be added. Suitable electrolytes are potassium chloride, sodium nitrate, potassium nitrate, sulphates or any strong, substantially neutral electrolyte. The moisture in the medium may be controlled by using a mixture of hygroscopic and non-hygroscopic electrolytes. Potassium chloride which is comparatively non-hygroscopic may be mixed with varying amounts of sodium nitrate which is hygroscopic to produce a desired moisture retaining characteristic. Many other combinations will be evident to produce this result.

Paper or other supports coated or impregnated according to the above process and variations of the process or with the above substitutes are inbismuth and/or molybdenum and/or 'stannic pounds set forth above to improve the quality Starch or compounds from substantially white or colorless compounds to colored lower oxides or the elements themselves at the cathode of an electrical circuit. For use in facsimile, the supporting sheet is fed so that facsimile signals may be passed between two electrodes thru the medium causing marking. While the coatings set forth herein are not'limited by the use to which they are put, still it is pointed out that they are not substantially afiected by heat or light. Hence, we may characterize the above coatings by sayingthat The odd series of Group V of the periodic table, includes arsenic, antimony and bismuth. The characteristics of antimony and bismuth compounds in an electrical recording system have been described. Arsenic compounds, while representing differences in some of their characteristics, have been found to be reducible by an electric current to a dark-colored compound.

Arsenic trisulphidaAszSs, arsenic trioxidaAszOs, and arsenic oxide, A5205 were separately tried by coating on a supporting sheet, rendering electroconductive and passing an electric current thru the coating. A dark marl: appeared at the oathably more acid than the equivalent oxychlorides of antimony and even more so than the oxychlorides of bismuth. The cxychlorides of arsenic readily decompose in Water to the trioxide as is to be expected from their more acid nature. The disadvantage of arsenic is its intensely poisonous character, especially arsenic trioxicie,

AS303. In general, arsenic compounds are the 1 equivalent of antimony and bismuth compounds except that they are more poisonous, more, soluble and more acid.

A large number of arsenic, antimony and, bismuth compounds suitable for electro-chemical marking by reduction at the cathode of an elecacer ic tric circuit have been set forth. While some of these compounds are colored and others reduce with difllculty, they are as a class suited to such marking as above described. Many other compounds of arsenic, antimony and bismuth are known to exist. This disclosure of many readily available compounds is considered to be a. disclosure of other compounds of these elements not noted which have similar desirable characteristics. Therefore the invention is limited only by the spirit and scope of the appended claims.

. While not in any way intended to limit the invention, the following specifications have been found to be desirable.

With electrode areas of 0.0003 square inches; paper 0.0025 inch thick, the best operation has been obtained when operating at a surface speed of 30 incheaper second when the medium had a resistance between 100 and 1000 ohms. Papers with resistances as high as 100,000 ohms may be useful, but, in general, at resistances of the order of rooaooo ohms or greater between the above specified. electrodes the paper breaks down before sufficient current to produce a maria can be passed.

What is claimed is:

1 An electrolytic recording material which comprises a supporting surface carrying an electrolytically sensitive composition consistins essentially of a compound of the class consisting of, antimony trioxide, antimony oxysulphate, potassium antimoniate, tartar emetic, antimony pentasulfide, bismuth oxynitrate, bismuth oxyiodogallate, bismuth subgallate, bismuth salicylate (basic), bismuth lactate, bismuth chromate, bismuth trioxide, bismuth tetraoxide, bismuth ammonium citrate, bismuth citrate, bismuth phosphate, bismuth oxalate, and bismuth tannate, and an electrolyte in sufiicient quantity to make the material conducting in the presence of water.

2. An electrolytic recording material which comprises a supporting surface carrying an electrolytically sensitive composition consisting essentially'of a compound of the class consisting of, antimony trioxide, antimony oxysulphate, potassium antimoniate, tartar emetic, antimony pentasulfide, bismuth oxynitrate, bismuth oxyiodogallate, bismuth subgallate, bismuth salicylate (basic), bismuth lactate, bismuth chromate, bismuth trioxide, bismuth tetraoxide, bismuth ammonium citrate, bismuth citrate, bismuth nate, a buffer chosen from the class consisting of, gallic acid, salycilic acid, benzoic acid, citric acid, boric acid and phosphoric acid, and an electrolyte in sufilcient quantity to make the material conducting in the presence of water.

PAUL TAIMEY. 

